Spacer for use in supporting lens blank during finishing



Jan. 20, 1970 R. K. LANM'AN I 3,490,182

SPACER FOR USE IN SUEPORTING LENS BLANKD'URING FINISHING Origin-a1 Filed Feb. 26, 1965 ,Q05EE7' K (AA/MAN INVENTOR.

ATTdQ/VE) United States Patent 3,490,182 SPACER FOR USE IN SUPPORTING LENS BLANK DURING FINISHING Robert K. Lanman, Pasadena, Calif., assignor to Armorlite Lens Company, Inc., Burbank, Calif., a corporation of California Original application Feb. 26, 1965, Ser. No. 435,529, now Patent No. 3,355,342, dated Nov. 28, 1967. Divided and this application July 17, 1967, Ser. No. 653,913

Int. Cl. B24b 13/02 US. Cl. 51-216 5 Claims ABSTRACT OF THE DISCLOSURE A set of precision spacers for use to space an unfinished lens blank in a desired position to facilitate bonding the same to a lens block while finish-grinding the upper surface of the blank to precise prescription requirements.

This application has been divided from applicants copending application for United States Letters Patent Ser. No. 435,529 filed Feb. 26, 1965, entitled Method of Supporting Lens Blanks for Grinding and Polishing, now Patent 3,355,342 granted Nov. 28, 1967.

This invention relates to the lens finishing and grinding art and more particularly to an improved method and technique for mounting and supporting a plastic lens blan-k in a lens holder with greater precision while avoiding numerous undesirable factors present in lens anchoring techniques used heretofore. The invention utilizes a plurality of small spacer elements of uniform thickness appropriately and equitably distributed about the outer portion of each lens blank supporting area and effective to assure precision anchorage of a lens blank to a supporting lens block therefor while being ground and polished. The spacers preferably have a thickness corresponding to that of the bonding layer employed to anchor the blank to the lens block. Also one face of the spacers may and preferably is coated with an adhesive film, such as a pressure sensitive type, to expedite and facilitate use of the spacers without risk of their movement after being placed in a desired position on the face of the lens block. Also featured by the invention is a bonding adhesive having negligible shrinkage and exothermic heat during setting.

According to prior technique it has been common practice to anchor a lens blank against the surface of a lens holder while subjecting its outer exposed surface to finish grinding and polishing. Anchorage of the lens blank to the holder has been performed in the main by waxes, paraffin, and various adhesives distributed as a layer between the parts. Many problems attend the use of these various materials. Among these adverse factors is the fact that these various anchoring materials require heating of fusible material or evolve exothermic heat while taking a set. This temperature change heats the blank unequally setting up undesirable strains and stresses within the lens blank and cause distortion. These undesirable consequences are augmented by difliculties attending the unequal distribution and unequal thickness of the bonding layer sandwiched between the lens blank and the lens block. It is most diflicult to obtain a bonding layer of uniform thickness as is desirable except by the use of costly complex blocking machines. Commonly used bonding materials are also subject to shrinkage and if the layer is thicker in one area than in another, unavoidable dilferential shrinkage occurs and this can result in serious consequences for obvious reasons. Another problem arises from the presence of volatile constituents in many bond- 3,490,182 Patented Jan. 20, 1970 ing agents. These can escape but slowly from the rim of the layer thereby greatly prolonging setting.

By the present invention the foregoing and other serious disadvantages of prior lens supporting techniques are substantially avoided or entirely eliminated. To this end, there is utilized a plurality of thin flexible spacer members having a thickness corresponding to the desired thin layer of bonding material. The diameter or width of these spacers is a small fraction of the diameter of the lens block and preferably, the lower surface is coated with a film of pressure sensitive adhesive to expedite their accuracy and immovable mounting against the surface of the lens block. In consequence, the spacers are not subject to displacement as by contact with the operators fingers while positioning other spacers or by the bonding agent itself as the latter spreads out over the block surface.

An important feature of the invention is the use of a bonding agent having negligible shrinkage and which takes a set without any material temperature change. Additionally, the bonding agent is characterized by the absence of a solvent or other constituent which vaporizes while the c nstituents take a set.

Additionally, the preferred bonding agent used with the present technique is transparent enabling the operator to view the locator guide marks customarily present on the surface of the lens holder and used to orient the lens blank in a predetermined relation to the holder thereby facilitating grinding the upper surface to meet prescription requirements.

Accordingly, it is a primary Object of the present invention to provide an improved precision method for supporting lens blanks in lens holders during grinding and polishing operations.

Another object of the invention is the provision of an improved mode of supporting a lens blank in a lens holder characterized by the use of a plurality of identical flexible spacer elements corresponding in thickness to the thickness of the bonding layer and enabling the operator to gauge the thickness of this layer quickly and with precision during the assembly of the blank to the holder.

Another object of the invention is the provision of an improved technique for holding a lens blank to a lens holder utilizing gauging spacers between the parts and a bonding agent having negligible shrinkage and taking a set substantially without a change in temperature. temperature.

Another object of the invention is the provision of identical precision flexible spacer elements suitable for use by lens grinders in accurately positioning and supporting a lens blank while the blank is being subjected to grinding and polishing.

These and other more specific objects will appear upon reading the following specification and claims and upon considering in connection therewith the attached drawing to which they relate.

Referring now to the drawing in which a preferred embodiment of the invention is illustrated.

FIGURE 1 is a top plan view with parts broken away and showing the lens blank supported on a lens block in accordance with the invention;

FIGURE 2 is a cross-sectional view taken along line 22 on FIGURE 1; and

FIGURE 3 is a fragmentary sectional view taken along line 3-3 on FIGURE 1.

Referring to the drawing, there is shown one preferred embodiment of the facilities for practicing the present invention using a typical conventional lens block 10. It will be understood that these blocks diifer in size and, in particular, as respects the contour of its upwardly facing surface 11 which is contoured to mate generally with the previously finished lower face of the blank to be finish-ground on its upper face. As here shown, surface 11 is generally concave and conforming generally with the downwardly facing surface 16 of the lens blank 12 the upper surface 17 of which is to be finish ground. The main body of block includes a shank 13 provided axially of its undersurface with a hardened center cone 14 to receive the grinding machine drive pins of conventional grinding equipment.

To be noted is the fact that holder 10 preferably has a size somewhat larger than the blank to be finished. In consequence the upwardly facing surface 11 of the block underlies the entire lower surface 16 of blank 12 even though the blank is supported slightly offcenter as often required by the prescription specifications. It will be understood that lens blank 12 is usually cast from suitable plastic materials with one surface, as 16, cast exactly to shape and with a surface so smooth as to require no additional processing. Such blanks as cast, are sufficiently thick to permit the opposite surface 17 to be finished and ground to a desired shape to satisfy a particular prescription requirement.

It will be understood that surface 11 of the lens block customarily is provided with suitable guide or reference lines by which the lens blank can be mounted in the holder in a predetermined position or orientation, thereby enabling the operator to grind surface 17 in exact correlation to surface 16. Such guide means, as here illustrated, comprise a shallow long groove 18 extending diametrically of the holder and a second shorter groove 19 passing through the center of the holder at right angles to groove 18. A typical mode of utilizing these guide grooves will be explained in connection with FIGURE 2 and the mounting therein of a lens blank 12 for use in making bifocal spectacles. For this purpose blank 12 is cast with a bulge or raised area 21. This area occupies a portion of the lower half of the finished lens with the peripheral surface areas merging smoothly and imperceptibly with the adjacent surface area 16 of the lens proper. It will be understood that, by use of grooves 18 and 19, the operator assembling the blank in holder 10 can position this raised area 21 in a precise angular location relative to one quadrant of the holder as defined by intersecting guide grooves 18, 19. This orientation operation is performed before the bonding agent takes a set and enables the operator to know with certainty the position of special contours on lower surface 16, such as bifocal portion 21, while grinding upper surface 17.

Referring now more particularly to FIGURE 1 it is pointed out that an important feature of the invention comprises use of a plurality of identical precision spacer elements 25, 25. These are relatively small in width as compared to the diameter of block 10, a width of 150 to 150 mils being suitable. The thickness of the spacers corresponds to the thickness desired for bonding layer 27. This layer is normally very thin in order to minimize the adverse effects of the slightest shrinkage and temperature change. In the case of a blank having bifocal capabilities a somewhat thicker layer of adhesive is appropriate and, in this case, a thicker spacer is employed.

Spacers 25 are formed of thin flexible material capable of being calendered accurately to uniform thickness. Flexible sheet plastic material is excellent for this purpose as for example, polyvinyl chloride and polyethylene. This material conforms readily to a wide range of lens holder and lens blank contours between the surfaces being bonded together. Desirably one surface of spacers 25 is provided with a film of pressure sensitive adhesive for use in holding the spacers in a selected position on surface 11.

In practicing the present technique the operator selects a holder 10 having an upper surface corresponding generally to that of the lens blank to be finish ground. Making certain that the upper surface of holder 10 is clean. the operator supports this holder firmly in an upright position with surface 11 facing upward and applies a spray coating to form an adhering film 28 to both surface 11 and surface 16 of the blank. Suitable material for this film is commercially available and comprises cellulose acetate butyrate as a principal constituent and a plasticizer to provide a separable bonding film between the epoxy resin layer and the adjacent surfaces of the lens block and the lens blank. Without this film the epoxy tends to adhere to the parts too tenaciously whereas the presence of the described film assures adequate holding power while permitting the parts to be separated after polishing by chilling followed by light tapping or slight flexing.

The operator then proceeds to apply three or four of the spacers 25 to surface 11 at points spaced uniformly from one another and from the outer rim edge of the holder. A suitable position is that shown in FIGURE 1 wherein four of the spacers are shown. As there illustrated the spacers are located along the bisectors of the respective quadrants formed by guide grooves 18, 19. Alternatively and particularly when mounting a bifocal lens blank, spacers 25 are preferably applied to surface 16 with care being exercised to locate the spacers to either side of the raised bifocal segment. The blank may then be rotated and oriented with respect to the guide lines.

Having located the spacers on coated surface 11 or 16, the operator proceeds to pour an accurately measured quantity of adhesive material having the characteristics identified above into the center of concave surface 11. A suitable bonding agent providing excellent results is an epoxy resin such as Epon 815 from Shell Chemical Co., or the epoxy resin made by Pace Products Co., Chicago, Ill. Both adhesive products have negligible shrinkage during setting, no solvents which vaporize during setting. Both set with negligible temperature change. This measured quantity of adhesive is preferably slightly in excess of that required to form a layer 27 coextensive with surfaces 11, 16 and corresponding to the thickness of spacers 25 when the adhesive is distributed uniformly between these surfaces. Initially, the quantity of the adhesive poured into the holder is located well inwardly of spacers 25. Thereafter the operator orients blank 12 to the ground to its approximate position and lowers it toward the holder with its finished surface 16 lowermost. The final phase of the lowering operation progresses slowly as the blank contacts the pool of adhesive and spreads radially outward past spacers 25. The adhesive does not pass into contact with the upper surface of the spacers owing in part to the proximity of these surfaces to blank surface 16 and in part to the surface tension of the adhesive. Accordingly, there is substantially no opportunity or risk that the tops of the spacers will be contacted by the adhesive.

No air bubbles are entrapped because all air is forced outwardly ahead of the advancing rim of the adhesive pool. Any excess adhesive overflows the rim of the holder and may be caught by an underlying receptacle. Once the blank is in contact with spacers 25, the operator checks to make certain that the center line through area 21, or other reference line, coincides exactly with the axis of one of the grooves, as 19, and then presses the blank firmly and equally against each of the spacers. It is then known that the adhesive is uniformly distributed and of uniform thickness except in the area underlying the bifocal raised portion 21.

The assembled parts are left in this position for the short period required for the adhesive to take a set at room temperature and without any material change in the temperature of the adhesive itself. The time period for setting varies with the particular adhesive used. Once setting is complete, the operator may proceed im mediately with the grinding and polishing operation with full knowledge that the lens blank is not distorted or under strain or stress either by shrinkage of the adhesive or by unequal temperature conditions within the blank. Following completion of the grinding and polishing operation the parts are disassembled in known manner, the adhesive layer is cleaned away from the parts and the lens is ready for mounting and use and the holder reused in finishing innumerable other blanks.

It will also be understood that it is a feature of this invention to employ spacers 25 of differing thicknesses and employed in a desired combination to enable the grinder to grind a lens blank having prismatic characteristics with one edge thicker than the diametrically opposed edge. It will be recognized also that four of the spacers may be located at the corners of a square, and equally distant from the axis of a lens blank having a cylindrical surface.

While the particular spacer for use in supporting lens blank during finishing shown and disclosed herein in detail is fully capable of attaining the objects and providing the advantages hereinbefore stated, it is to be understood that it is merely illustrative of the presently preferred embodiment of the invention and that no limitations are intended to the details of construction or design herein shown other than as defined in the appended claims.

I claim:

1. That improvement in a lens block having a thin layer of adhesive for anchoring an unfinished lens blank in a desired position thereon while finish-grinding the upper surface of the lens blank to precise prescription requirements which comprises a set of removable spacers comprising a plurality of similar one-piece wafers blanked fro mthin flexible sheet material of predetermined thickness corresponding to the thickness of said thin layer of the particular adhesive employed to anchor an unfinished lens temporarily to said lens block during the finishgrinding operation, said spacers having a transverse dimension of the order of to mils, and a thin film of pressure sensitive adhesive on one surface of said spacers effective to hold said spacers firmly seated selectively in a desired position on the face and near the rim of said lens block while said layer of adhesive is being distributed over the surface of the lens block to a thickness determined by the thickness of said wafers.

2. That improvement defined in claim 1 characterized in that said spacers comprise identical gauge components of identical thickness, and said spacers having a transverse dimension which is a small fraction of the transverse dimension of the lens block on which said spacers are to be used.

3. That improvement defined in claim 2 characterized in that said wafers are circular.

4. That improvement defined in claim 1 characterized in that each thereof is of the same thickness.

5. That improvement defined in claim 1 characterized in that at least one wafer is of a slightly different thickness than another one thereof and adapted to cooperate with one another to support a lens blank having one edge thicker than another by a layer of adhesive of more nearly uniform thickness than is possible using spacers of uniform thickness.

References Cited UNITED STATES PATENTS 2,608,503 8/1952 Meyer 161-406 X 3,140,568 7/1964 Beasley 51277 X 3,190,788 6/1965 Loos 161406 X HAROLD D. WI -IITEHEAD Primary Examiner 

